The present invention relates to a method and device for vacuum-coating a substrate.
A method of this type is described in German Patent No. 195 13 614. According to this patent, the coating of a substrate with amorphous layers of carbon takes place through the application to the substrate of a bipolar voltage whose positive and negative pulse durations can be adjusted separately from one another. During the depositing, the positive pulse duration is smaller than the negative pulse duration, and the pulse frequency is in the range from 5 to 100 kHz. In order to improve the adhesion of the produced amorphous carbon layer to the substrate, is applied a modified carbon intermediate layer that contains metal. In this conventional method, plasma production and ion bombardment of the growing layer are realized together using the applied bipolar voltage, and cannot be controlled individually. For many qualities of layer, the layer deposition using this process is therefore limited to a comparatively narrow process window.
From the German Patent No. AZ 196 09 804, a method is described for the plasma coating of bulk material in which a rotating basket moves slowly about a plasma coating source. A voltage can be applied to the rotating basket in order to bring the bulk material to be coated to an electrically negative potential. Means for producing a cleaning plasma, with which the bulk material is cleaned before the beginning of the layer deposition, are located inside the rotating basket. In this context, the cleaning plasma is produced independently of the voltage applied to the rotating basket and to the bulk material. A negative electrical charging of the bulk material to be coated is in general also provided for the subsequent coating step. No further indications are disclosed concerning the manner in which the negative charging is to take place.
A method for the manufacture of hard amorphous carbon layers is described in R.S. Bonetti, M. Tobler, xe2x80x9cIndustriell hergestellte diamantartige Schichten,xe2x80x9d Oberflxc3xa4che und JOT, vol. 9, 1988, p. 15. In a plasma-supported CVD method, plasma production and negative substrate bias voltage are realized together, using a radio-frequency (RF) power supply applied to the substrate. The substrate potential ensures the ion bombardment required for the depositing of layers that are dense and hard and therefore resistant to wear. For this purpose, the ratio between the surface of the parts to be coated and the inner wall surface of the recipient must be smaller than 1, which limits, in an undesirable manner, the charge density and ability to scale the method upward for industrial charge quantities. Another disadvantage is the required load-dependent matching of the RF coupling.
An object of the present invention is to indicate a method and device scaled upward and that can be used for industrial charge quantities, which permits the coating of substrates uniformly and at a high rate, and produces a mutitlayer structure that is wear-resistant and that reduces friction.
The object is achieved due to the separation of the production of the substrate voltage from the production of the plasma. The present invention allows a well-directed influencing of the physical properties of the produced layers. Among others, the layer hardness, the ability to withstand abrasion, the elasticity of the layer and the internal stress of the layer can be influenced. Substrates having complex geometries can also be coated. In this context, the separation of plasma production and substrate voltage production allows a controlling of the substrate temperature. In this way, the layer deposition can take place in multiple fashion at temperatures of 200xc2x0 C. and lower. As a substrate voltage, a pulsed bipolar direct voltage is advantageously used that can be changed with regard to the size and duration of the negative impulse, the size and duration of the positive impulse, and the voltage-free intermediate intervals, that is, pause periods. In order to expand the possible achievable layers, the addition of various process gases in suitable mixture and sequence is usefully provided.
The separation of plasma production and substrate voltage production does not limit a device suitable for the execution of the method to the use of a particular plasma production source. Rather, all plasma-producing sources, such as microwave sources, high-frequency sources, hollow cathodes or high-current arcs, are possibilities. As a power supply for the production of the substrate voltage, a direct-voltage power supply pulsed in bipolar fashion is useful, making it possible to support a direct voltage and realize voltage-free pause periods. Screens that shield a part of the coating chamber are advantageously provided in the coating chamber. The properties of the produced layers can be influenced easily by moving the parts to be coated through the resulting partial volumes, which have different plasma densities, that arise in this context.
A multilayer structure manufactured according to the present invention has the considerable advantages that it is made up of alternating layers of hard material and hard carbon layers, the latter additionally containing, if necessary, oxygen and/or silicon and/or metal. In the structure, the resistance to wear of the hard material, and in particular the outstanding resistance to wear and friction-reducing lubricating effect of the inventively manufactured hard carbon, work together synergistically with the multilayer structural properties. The multilayer structure has, for example, a greater hardness than the individual layers of which it is made. Moreover, the multilayer structure is more ductile and more elastic than an individual layer of comparable hardness.
Due to the synergistic cooperation of the above-cited properties, the multilayer structures manufactured according to the present invention can advantageously be used in new areas of application. Thus, they are generally suited for use as protection against corrosion and wear for components that are tribologically highly loaded, and are suited, in particular, for use as wear protection of components in situations of dry operation and lack of lubrication. For example, the multilayer structures are suitable for use as a lubricating anti-wear and anti-corrosion layer for machining tools and non-cutting shaping tools, whose lifespan are increased considerably in this way, they enable dry processing or processing with minimal lubrication using tools coated therewith, so that cooling lubricants can be done without entirely lubricating the dry process, or at least the quantity of lubrication required can be greatly reduced. In addition, the coating with multilayer structures manufactured according to the present invention enables improvement of the protection against corrosion of components in aggressive media, and, if coated tools are used, the processing speed and processing quality of components can be raised.
It is advantageous if the carbon layer is made of amorphous carbon containing hydrogen (hereinafter a-C:H), amorphous hydrogen-free carbon (a-C), carbon (containing hydrogen or hydrogen-free) containing silicon, or carbon (containing hydrogen or hydrogen-free) containing metal (C-(MeC)). The metal is selected from the hard secondary group metals. This selection enables the user to react flexibly to demands that are made with regard to the lubricating action and the hardness of the carbon layer, and (see above) to possible difficulties of adaptation to the hard material layer.
Alternatively, instead of the carbon containing silicon layers, additional layers containing, if necessary, hydrogen and/or carbon and/or metal, can be built into the multilayer coating. It is true that these have no lubricating effect, but they are also characterized by a high degree of hardness (even if as a rule they are somewhat softer than carbon layers) and lower friction coefficients. A particular advantage is the low degree of dependence of the layer properties, in particular the friction coefficient, on the ambient humidity.
It is advantageous if the silicon layer is made of amorphous silicon containing hydrogen (hereinafter a-Si:H), amorphous hydrogen-free silicon (a-Si), silicon (containing hydrogen or hydrogen-free) containing carbon, or silicon (containing hydrogen or hydrogen-free) containing metal (Si-(MeSi)). As with carbon, this selection makes it possible in particular to react flexibly to demands.
A multilayer structure of hard layers, lubricating layers and, if necessary, oxidation-resistant layers, the properties of the structure are determined by the combination of the properties of the individual layers, is described in U.S. Pat. No. 4,619,865, but hard carbon or silicon layers, or hard carbon or silicon layers containing the metals named, are not described in the patent, in particular not as friction-reducing layers.
With respect to their composition, the individual layers are preferably made of one type, or several types, of the hard material layer, and one type, or several types, of the carbon layer or the silicon layer. The individual layers are made up most preferably of one type of the hard material layer and one type of the carbon layer or the silicon layer.
In order to exploit optimally the advantages of the multilayers, it is advantageous if the thicknesses of the individual layers are between approximately 1 nm and approximately 10 nm, and preferably between approximately 2 nm and approximately 5 nm, and if the overall thickness of the structure is between approximately 1 xcexcm and approximately 10 xcexcm, and preferably between approximately 1 xcexcm and 4 xcexcm.
It is advantageous if the hard material layer is made up of a metal (hereinafter Me), a metal compound, carbon containing metal carbide (C-(MeC)), silicon containing metal silicide (Si-(MeSi))xe2x80x94the latter two materials having, among other things, the desired hardness due, for example, to a corresponding selection of the metalxe2x80x94or mixtures of at least two of the named materials. This selection makes it possible for the user to react flexibly to demands relating to the hardness of the hard material layer, and possible difficulties of adaptation to the carbon layer or the silicon layer, andxe2x80x94if advantageousxe2x80x94also additionally to equip the layer with a certain friction-reducing effect.
Advantageous combinations of the hard material layer and the carbon layer result if the hard material layer is made of Me, a metal carbide (MeC), a metal nitride (MeN), a metal silicide (MeSi), a metal carbonitride (Me(CN)), a metal carbosilicide (Me(CSi)), or a metal siliconitride (Me(SiN)), and the carbon layer is made of a-C:H or a-C; if the hard material layer is made of C-(WC) and the carbon layer is made of a-C:H, the hard material layer having a high degree of hardness due to the use of tungsten, but also having a considerable lubricating effect due to the carbon portion, which is not bound chemically to metal; and if the hard material layer is made of MeC and the carbon layer is made of C-(MeC), the hardness being particularly pronounced here, though at the cost of the lubricating effect.
Advantageous combinations of the hard material layer and the silicon layer result if the hard material layer is made of Me, MeC, MeN, MeSi, Me(CN), Me(CSi), or Me(SiN), and the silicon layer is made of a-Si:H or a-Si.